1. Field of the Invention
This invention relates to processes for the production of mixtures of potassium phosphates and potassium polyphosphates from phosphate rock or a solubilized form, sulfuric acid and potassium hydrogen sulfate wherein the reaction may be carried out in a continuous manner.
2. Description of the Prior Art
In the first application above-identified of two of us, there are disclosed and claimed potassium polyphosphate products, processes for preparation of mixtures of potassium dihydrogen phosphate and potassium monohydrogen phosphate and the treatment of these mixtures by heating at an elevated temperature to produce a novel reaction product mixture having variable water solubility and variable molecular weight, which mixture is eminently suitable as a fertilizer material. In this prior application, there are disclosed procedures for the preparation of these mixtures which generally comprise reaction of an acid such as phosphoric acid or sulfuric acid or mixtures thereof with phosphate rock or a solubilized form in the presence of potassium sulfate or potassium hydrogen sulfate at temperatures in the range of about 40.degree. to 90.degree.C. The second-named application of two of us provides refinements on this basic process. The present invention provides an improved and refined process for the preparation of the desired intermediate potassium phosphates wherein the phosphates may be prepared in a purity suitable for use as an intended fertilizer or for further conversion to potassium polyphosphate products.
Various processes are known in the prior art for the reaction of phosphate rock and an acid such as sulfuric acid or phosphoric acid or mixtures thereof, processes of these types being referred to generally as phosphate rock acidulation. Quite often potassium sulfate, and in some cases, potassium hydrogen sulfate, may be added to precipitate the calcium present in the mixture as calcium sulfate. These patents are for example, U.S. 1,866,657, 2,046,829, 1,747,588, 744,128, 1,037,837, 1,447,544, 2,046,841, 2,046,842 and 1,961,127. However, these processes fail to provide fertilizers sufficiently pure to be useful in the intended area of use. Moreover, these patents fail to provide workable processes for conducting the reaction in an economical manner.
It is therefore clear that a distinct need remains in the art for procedures by which the desired potassium phosphates can be prepared in an amount and purity sufficiently high that they can be used for the purposes set forth in our above-identified copending application. Our last-mentioned application discloses and claims a number of improvements in this area. The process of the present invention meets these objectives and also provides a more refined and improved process over that disclosed and claimed in out last-mentioned copending application.